1. Field of the Invention
This invention generally relates to particle populations, assays, and methods for processing assays.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
Fluid assays are used for a variety of purposes, including but not limited to biological screenings and environmental assessments. Often, particles are used in fluid assays to aid in the detection of an analyte of interest within a sample. In particular, particles provide a substrate for carrying a reagent configured to react with the analyte of interest within a sample such that the analyte may be detected. In some cases, a multiplexing scheme is employed in assay analysis systems such that multiple analytes may be evaluated in a single analysis process for a single sample. To facilitate a multiplexing scheme, particles are configured into distinguishable groups and each group is used to indicate the presence, absence, and/or amount of a different analyte in an assay. The different particle subsets may be distinguishable, for example, by different fluorescent dyes and/or different concentrations of dyes absorbed into particles and/or bound to the surface of particles. In addition or alternatively, the size of particles among the different subsets may vary. In any case, the number of particles within each particle subset is typically very similar if not the same within an assay. As a consequence, the range of concentrations that can be detected and/or quantified for an assay are generally the same for each analyte of interest.
In some cases, however, it may not be advantageous to analyze all analytes of interest within an assay relative to the same detectable range. On the contrary, in cases in which two or more analytes of interest are present in a sample at significantly different concentrations, it may be advantageous to analyze each analyte of interest relative to a different detectable concentration range such that more comprehensive and accurate analysis results may be obtained with respect to each analyte of interest. However, in order to implement such specificity, the ability to multiplex a sample may be hindered. In particular, a more favorable protocol for the detection and quantification of an analyte of interest in great abundance in a sample includes diluting the sample in order to spread the captured analyte of interest over a greater number of particles and then analyzing each of the dilutions separately to get a reporter response that is within the dynamic range of the detection system. In contrast, a favorable protocol for the detection and quantification of a rare analyte of interest avoids any dilution of a sample in order to maintain the reporter response per particle for the analyte of interest and improve the limit of detection of the analyte of interest. Given the conflicting processing steps of dilution versus no dilution for the different analytes of interest, it is not possible for the two analytes of interests to be analyzed in a multiplex scheme with such protocols.
An alternative approach for facilitating a different detectable range for each analyte of interest within a sample which preserves the use of a multiplex scheme is to employ widely different concentrations of particles among different particle subsets in an assay. In particular, it may be advantageous to have a particle subset with a reactant for an analyte of interest in great abundance in a sample to have a greater concentration of particles within an assay than a particle subset with a reactant for a rare analyte of interest. In this manner, the analyte of interest in great abundance may be spread over a greater number of particles and the reporter response per particle for the rare analyte of interest may be increased. This approach, however, may hinder the ability to obtain accurate results for each analyte of interest when particles are analyzed in batches, such as done in static imaging systems. In particular, the ratio of particles immobilized on an imaging plane for analysis within a static imaging system will generally follow the concentration of particles comprising particle subsets of the assay. Thus, the imaging plane will be populated preferentially with the particle subset/s of relatively higher concentration. In some cases, the particle subset/s of relatively lower concentration may not be present in enough quantity to be statistically significant and, thus, substantive results may not be obtained for the analyte of interest/s associated with the particle subset/s of relatively lower concentration.
Accordingly, it would be desirable to develop methods, systems, particle populations, and assays that allow particles of a particle subset having a relatively lower concentration of particles to be preferentially captured in an imaging chamber over another particle subset having a relatively higher concentration of particles in order to compensate for the difference in particle concentrations dictated by an assay protocol.